[30.04] The Clump Spectrum of Two High-Latitude Molecular Clouds

Leo Blitz, Marc W. Pound (UMD)

We have applied the clump-finding program of Williams et. al.
(1994) to two high galactic latitude molecular clouds. The data
consist of large-scale, well-sampled $^{13}$CO(1-0) and CO(1-0) maps of the
high-latitude clouds MBM12 (=L1457) and MBM41-44 (Draco Nebula),
and have about 500,000 pixels each. This is the first application
of the clump-finder to HLCs as well as to large datasets.
In each cloud, we find more than 200 clumps ranging from a few hundredths
of a solar mass to a few solar masses. We derive the total mass of
MBM12 to be 150 ${\rm M_{\sun}}$ and of MBM41-44 to be 140 ${\rm M_{\sun}}$.
In both clouds, the high sensitivity of
the maps allow determination of the mass spectrum including
substellar mass clumps ($M < 0.08~{\rm M_{\sun}}$).
We find that the clump mass spectrum in MBM41-44 has power-law
index $\alpha=1.40~\pm~0.06$, similar to that found for giant
molecular clouds. MBM12, however, has a shallower spectrum,
$\alpha =1.07~\pm~0.05$. (The quoted errors are statistical uncertainties.)
It is surprising that the clump mass spectrum
for MBM41-41, a cloud complex far from being gravitationally bound,
has the same mass spectrum as the Rosette complex, a well-studied
giant molecular cloud.

We compare the derived HLC quantities to the results of Williams etal for
the Rosette molecular cloud. We find that the HLCS have a significantly
steeper size-linewidth relation than the Rosette
($\Delta V \sim R^{0.7}$ for HLCs; $\Delta V \sim R^{0.4}$ for the Rosette).
We describe a method to determine the internal clump density profile
for pressure-bound clumps from the size-linewidth relation. In principle,
this method will work even for unresolved clumps.
Finally, we report the discovery of a new cloud in the Draco Nebula ``chain.''